(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of eliminating errors in measuring overlay that are caused by metal deposition asymmetry before metal etching.
(2) Description of the Prior Art
Continued emphasis on semiconductor device reduction has placed increased emphasis on the alignment of the overlying patterns that are required for the creation of a semiconductor device. Such patterns are typically created using a photolithographic process in which a pattern of the circuit is transferred from a microscopic scale onto the surface of a substrate where the pattern becomes part of a semiconductor device.
In order to enhance device throughput, a typical photolithographic process uses a step-and-repeat function for the transfer of the pattern that is contained in the mask to the surface that is being exposed. A number of errors and inaccuracies-can be introduced during this exposure process, it is for instance of key importance that overlying layers of material that are to be processed are exactly aligned with each other since misalignment leads to serious concerns of device performance and reliability. It is therefore of critical importance that overlay of the successive exposures is performed with an extreme degree of accuracy.
One of the methods that is used for measuring alignment of successive and overlying patterns is the box-in-box approach in which alignment aids are located at different areas such as the peripheral area of the surface of the substrate. The accuracy of alignment is then determined by comparing deviations in the centerlines of the box with a process average. For the performance of accurate alignment a number of these box-in-box patterns must be created in a number of locations on the die.
One of the problems that is encountered using the box-in-box technique is that asymmetric deposition of metal before an etch of one of the patterns of the box-in-box alignment marks introduces a measurement error. It has been observed that the measurement error for substrate scale alignment is about 0.3 to 1.0 ppm, which causes a 30 to 100 nm measurement difference between before and after metal etching. The invention addresses these concerns and provides a method that reduces the impact of asymmetric metal deposition on the accuracy of measuring alignment of overlying patterns of exposure.
U.S. Pat. No. 6,165,656 (Tomimatu) shows a box in box pattern error measurement method involving dummy patterns.
U.S. Pat. No. 5,952,132 (King et al.) shows a box in box pattern and error measurement method.
U.S. Pat. No. 5,870,201 (Bae) shows a box-In-box pattern and method.